Sensor integrated circuit with current output calibration

Abstract

A sensor integrated circuit configured to generate a sensor output current indicative of a sensed parameter includes a power connection to receive a supply voltage, a ground connection, a sensing circuit configured to generate a parameter current proportional to the sensed parameter, and an output connection at which the sensor output current is provided. An output current calibration circuit is configured to determine an offset current that corresponds to a bias voltage at the output connection equal to a fixed percentage of the supply voltage when the parameter current is substantially zero. The sensor output current is provided as a combination of the parameter current and the offset current.

What is claimed is: 
     
       1. A sensor integrated circuit configured to generate a sensor output current indicative of a sensed parameter, comprising:
 a power connection configured to receive a supply voltage; 
 a ground connection; 
 a sensing circuit configured to generate a parameter current proportional to the sensed parameter; 
 an output connection at which the sensor output current is provided; and 
 an output current calibration circuit configured to determine an offset current that corresponds to a bias voltage at the output connection equal to a fixed percentage of the supply voltage when the parameter current is substantially zero, wherein the sensor output current is a combination of the parameter current and the offset current. 
 
     
     
       2. The sensor integrated circuit of  claim 1  wherein the output current calibration circuit comprises:
 a voltage divider configured to generate a divided supply voltage equal to the fixed percentage of the supply voltage; 
 an operational amplifier coupled to receive the divided supply voltage and a voltage at the output connection and to generate a difference voltage; and 
 a voltage controlled current source responsive to the difference voltage and configured to generate the offset current. 
 
     
     
       3. The sensor integrated circuit of  claim 1  wherein the output connection is configured to be coupled to a resistor external to the integrated circuit. 
     
     
       4. The sensor integrated circuit of  claim 3  wherein the resistor is remotely located with respect to the sensor integrated circuit. 
     
     
       5. The sensor integrated circuit of  claim 1  further comprising a memory configured to store a setting indicative of the offset current. 
     
     
       6. The sensor integrated circuit of  claim 1  further comprising a memory configured to store information indicative of the supply voltage. 
     
     
       7. The sensor integrated circuit of  claim 1  wherein the sensing circuit comprises:
 a sensing element configured to generate a sensor output signal; 
 an amplifier coupled to receive the sensor output signal and configured to generate an amplifier output signal; and 
 a voltage controlled current circuit responsive to the amplifier output signal and configured to generate the parameter current. 
 
     
     
       8. The sensor integrated circuit of  claim 7  wherein the voltage controlled current circuit comprises a current source coupled between the supply voltage and the output connection and a current sink coupled between the output connection and the ground connection. 
     
     
       9. The sensor integrated circuit of  claim 8  wherein the sensing element comprises a magnetic field sensing element and the sensed parameter is a magnetic field. 
     
     
       10. The sensor integrated circuit of  claim 9  wherein the magnetic field is generated by a current flow through a primary current conductor. 
     
     
       11. The sensor integrated circuit of  claim 1  further comprising a circuit to check a level of the parameter current during operation of the output current calibration circuit. 
     
     
       12. The sensor integrated circuit of  claim 1  wherein the sensing circuit is disabled during operation of the output current calibration circuit. 
     
     
       13. The sensor integrated circuit of  claim 1  wherein the bias voltage is equal to one-half of the supply voltage. 
     
     
       14. A method for generating a sensor output current at an output connection of a sensor integrated circuit, comprising:
 applying a supply voltage to the sensor integrated circuit; 
 determining an offset current that corresponds to a bias voltage at the output connection equal to a fixed percentage of the supply voltage when a parameter current is substantially zero; 
 generating the parameter current proportional to a sensed parameter; and 
 providing the sensor output current at the output connection as a combination of the parameter current and the offset current. 
 
     
     
       15. The method of  claim 14  wherein determining the offset current comprises:
 dividing the supply voltage to generate a divided supply voltage corresponding to the fixed percentage of the supply voltage; 
 comparing the divided supply voltage to a voltage at the output connection to generate a difference voltage; and 
 generating the offset current based on the difference voltage. 
 
     
     
       16. The method of  claim 14  further comprising coupling the output connection to a resistor external to the integrated circuit. 
     
     
       17. The method of  claim 14  further comprising storing a setting indicative of the offset current. 
     
     
       18. The method of  claim 17  further comprising checking a level of the parameter current and using the stored setting indicative of the offset current to generate the sensor output current if the parameter current is greater than a predetermined level. 
     
     
       19. The method of  claim 14  further comprising storing information indicative of the supply voltage. 
     
     
       20. The method of  claim 14  further comprising disabling the generation of the parameter current during the determination of the offset current. 
     
     
       21. The method of  claim 14  wherein generating a parameter current comprises:
 sensing the parameter with a sensing element to generate a sensor output signal; 
 amplifying the sensor output signal to generate an amplifier output signal; and 
 generating the parameter current with a voltage controlled current circuit based on the amplifier output signal. 
 
     
     
       22. The method of  claim 21  wherein generating the parameter current with a voltage controlled current circuit comprises sourcing a current to the output connection or sinking a current from the output connection based on the amplifier output signal. 
     
     
       23. The method of  claim 21  wherein sensing the parameter with a sensing element comprises sensing a magnetic field with a magnetic field sensing element. 
     
     
       24. The method of  claim 23  wherein the magnetic field is generated by a current flow through a primary current conductor. 
     
     
       25. The method of  claim 14  wherein the fixed percentage of the supply voltage is one-half.